Method of making drawing dies



Aug., 20, 1940. E; w. ENGLE EVAL 2,212,394

' METHOD oF MAKING' DRAWING DIES Filed Dec. 16., 1957A /lu f A ORNEY Patented Aug. 20,

METHOD 0F MAKING DRAWING DIES y Edgar W. Engle, Noroton, and Hershel Bryan Duncan, Stamford, Conn., assignors to Carboloy Company, Inc., Detroit, Mich., a corporation of New York Application December 16, 1937, Serial No. 180,078

13 Claims.

The present invention relates to a method of making drawing .dies utilizing the class of materials known in the trade as cemented h ard metal 'carbides, such, for example. as the material described and claimed in the SchroterPatent No. 1,549,615, issued August 11, 1925, consisting of minute particles of extremely hard tungsten carbide cemented together with a small amount of cobalt. Such materials are characterized by very great hardness, compressive strength and resistance to abrasion, but do not possess sufficient tensile strength to withstand the-enormous forces set up in metal drawing operations such as the drawing of wire, rod, tubing and the like.

Drawing dies have heretofore been made by securing nibs of cemented carbide in casings of materials such as steel or bronze which possess high tensile strength and are-so designed and made as to reenforcethe cemented carbide nib. In prior practice it has been necessary to prepare the casing by accurate. machining and the nib by grinding and then to secure the latter within the former by brazing, or by shrink fitting, or by a forging operation as disclosed, for example, in the patent to Morris Simons, No. 1,952,388, issued March 2'7, 1934.

A general object of the present invention is the provision of an effective method for making such dies which may be readily and cheaply practiced in a minimum amount of time with a minimum amount of labor and material and which results in an efficient production of reenforced dies which are of simple .constructionand excellent quality, are capable of withstanding the enormous forces set up in .drawing operations, and have long lives.

A more specific object of the invention is the provision of an eiilcient method of providing such nibs with metal casings which gripthe nibs and place them under unusually high compression, eliminating the necessity of using supplemental drawing die holders, which `method eliminates the necessity of preliminary annealing of casing material and many machining operations and reduces to a minimum waste of material.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the several steps and the relation o`f one or more of such steps with respect to each of the others thereof, which will be exemplified in the method hereinafter disclosed, and the scope of the invention will be indicated in the claims.

For a fuller understanding of the nature and cbjectsof the invention reference should be had (Cl. 'I6-107) to the following detailed description taken in` connection with the accompanying drawing, in which:

Fig. 1 is a vertical sectional view of a forging die holder, associated structure and a blank or slug of casing material showinga nib and forging plunger in position" prior to a forging operation of the present invention;

Fig. 2 is a sectional view similar to Fig. 1 showing the nib forged into the casing blank or slug;

Fig. 3 is a similar sectional view showing the upper portion of the casing blank or slug forged over the upper end of the nib by a forging tool;

Fig. 4 is a vertical sectional view of a completed reenforced die;

Fig. 5 is a vertical `/sectional view similar to Figs. 2 and 3 with partsbroken away, showing a modified structure for forging the nib into the casing blank or slug in accordance with a variation of the method of the invention; and

Fig. 6 is a vertical sectional view withparts broken away of the forging die holder and casing slug with a nib forged therein, showing a modified form of bottom plate used in the forging die holder.

By the present invention a cemented hard metal carbide nib is forced directly into a slug or fiat blank of tool steel or other suitable material of high compressive strength, producing a ing to a large extent the machining and grinding\operations and waste of high priced material which is characteristic of the practices here-l tofore followed.

'I'he application of the present invention will be described with particular reference to the production of a wire drawing die having a nib of cemented tungsten carbide provided with a circular metal drawing passageway and surrounded by a casing of tool steel containing about .80%

to 1.05% carbon, about .20% to .45% vanadium and, if desired, up to about .5% chromium, though it is to be understood that the invention is applicable to the production of drawing dies of other designs, with nibs or other materials of the same class, and with casings of other materials having the necessary properties of high elastic strength and thermal expansion.

Cylindrical bar stock of the selected tool steel in unannealed condition is cut by means of an abrasive `wheel cutting machine into sections of predetermined length, with substantially fiat end faces. Each of these sections constitutes a casing slug or blank i0. Without further manipulation of any kind, each slug l0 is heated to a `drawing die of superior strength and eliminatsuitable forging temperature between about 1856 F. and 2000 F. to make it plastic. It is then transferred quicklyto a'cup-shaped forging die I I, formed of hot forging steel such as chromiumtungsten steel or other suitable material, in a press of the type adapted to deliver perc'ussive compression or a relatively slow hammer blow effect, such as a percussion, hydraulic or compression screw press. The forging die II preferably has the walls of the socket I2 therein tapered slightly and is provided with an ejection passage I3 in the bottom thereof to permit ready removal of a completed die assembly. A bottom plate Il, preferably formed of similar metallic material, is seated in the bottom of the socket I2.

A cemented tungsten carbide nib I5, without any preliminary finishing being required, is centered on top of the hot slug I0 and the press is operated to cause a press plunger I6 to drive or force the nib I5 into the slug I0 to the desired depth causing the nib to displace the slug material, preferably to an extent so that a portion thereof I1 projects above the upper end of the nib as shown in Fig. 2. Preferably the operation of the press is such that simultaneously or sequentially projecting portion of the slug material is caused to iiow over the outer portion of the upper end of the nib I5 as shown in Fig. 3.

The encased nib is then ejected from the forging die II, allowed to cool to about 800 F. and thereafter tempered at about 900 F. to 1250 F., preferably about 1150 F., to vdevelop the proper properties in the casing steel. After the tempering is complete, the casing material at the center of the bottom of the die is removed by a simple trepanning tool to form an opening I8. All that is necessary to finish the tool is to make and/or finish a wire-drawing hole I9 in the nib I5, to machine the outer surface 20 of the casing to insure concentricity with the hole I9 and, if desired, machine out opening 2| in the casing communicating with the wire-drawing hole.

If desired, although not necessary, the nib may have its surfaces ground and/or sand blasted to remove surface defects or adhesions prior to being forced into the casing slug and may be preheated. The nib forced into the casing slug may' be a blank nib or a cored nib, i. e. a nib provided with a wire-drawing hole. If a blank nib is used, it is preferably provided with a center 22 prior to being forced into the casing slug to permit readyA machining of the circumferential face of the casing concentric with the axis of the nib and to facilitate opening up the bottom of the casing. A bottom plate 23 provided with a suitable boss 24, frusto-conical in shape, may be used in the forging die II so that during forging an indentation will be formed in the bottom of the casing slug, as shown in Fig. 6. A similar indentation may be machined or'formed in the bottom face of the slug prior to the forging whereby such a bottom plate may be advantageously used to aid in centering the slug in the forging die.

The nib I5 may be centered on the hot slug I0 and suitably guided during forcing operation by a pair of centering tongs or by a centering ring 25 seatedwithin the socket I2 on the top of the hot slug I0. The portion of the casing material I1 which projects above the upper end of the nib I5 may be forged over the outer portion of the upper endof the nib in a variety of ways. In accordance with 'me method 'suggested inv Fig. 3, the plunger |6 is retracted and a forging plate 26 is substituted for the centering ring 25v The forging plate 26 preferably is provided with a fiat lower face and shaped to be received within the socket I2. A ange 21 may limit the downward movement thereof. The lower face of the plate 26 ils preferably provided with a circular boss 28 having a circumferential face curved smoothly to merge with the flat lower face to Vcause the projecting portion I1 of the casing material to flow over the outer portion of the upper end of the nib I5 and provide the opening 2| when compressive force is applied to the forging plate by the plunger I6 engaging in a recess 29 in the upper face thereof.

,As an alternative method of forging the projecting portion of the casing material over the outer portion of the upper end ofthe nib I5, the centering ring 25 may be omitted and the plunger I6 provided with an abutment located a suitable distance above the engaging end thereof so that as the nib is forced into the slug I0 the abut- 'ment causes the projecting portion I1 to flow inwardly over the outer portion of the upper end of the nib. Further alternatives are suggested in Fig. 5 by arrows, which may consist in restraining upward movement of the centering ring caused by upward movement of the projecting portion as the nib displaces slug material or the application of compressive force to the guide ring after it has been raised to a position similar to that shown in Fig. 2. A modied form of plunger' 30 may be used, the plunger being provided with a reduced end 3| shaped similarly to the boss 2B on the forging plate 26 in order similarly to shape the projecting portion I'I and the passage 2 I.

Materials other than tool steel may be used for the casing. Such materialsshould have high tensile strength and higher coefficient of thermal expansion than the nib material. Various types of bronze, suchl as aluminum bronze known as Avialite, satisfy these requirements. A suitable forging temperature for bronze is about 1500 F.

The casing slug may be heated to the forging temperature in a period of minutes. The slug I0 at the forging" temperature should flt easily into the socket I2 of the forging diel Il which preferably is cold when the heated slug is placed therein. Consequent chilling of the surface of the lslug eliminates any tendency forv it to weld to the socket face of the forging die.

By the present invention the manufacture of fled and the expense materially reduced. For example, the steel bar stock can be used in the unannealed condition, thus eliminating the expense of annealing which has heretofore been necessary. Preliminary machining of the casing material is entirely eliminated. Waste of the steel is eliminated with the exception of a very small amount which is trimmed from the casing after the forging operation is completed.k The preliminary grinding of the cemented tungsten carbide nib heretofore necessary to fit the nib to the machined casing is entirely eliminated. The amount of final grinding of the casing to vinsure its concentricity with the hole\in the nib is reduced to a minimum. y

In addition to the elimination of machining and grinding operations heretofer necessary and the elimination of waste, the present invention makes possible the production of drawing dies of superior strength and decreased liability to breakage in service.

As illustrative of the compression under which a nib is placed by the casing formed in accordance l cemented carbide drawing dies is greatly simpliwith the present invention in order to reenforce the nib against enormous forces set up by the drawing operations and thereby avoid likelihood of cracking the nib, the following test was carried out. A nib was forged into a steel casing in the manner described. Both ends of the ,casing were cut off to expose the full diameter of the nib. The assembly was then heated to 600 F. and mounted in an arbor press. It was impossible for two men to push the nib out of the casing with the press. The assembly was then heated to 900 F., replaced in the arbor press and two men succeeded in pushing the nib half way out of the casing but after the assembly had cooled olf it was impossible for them to push the nib further out of the casing.

In the claims the use of the terms hard metallic nib and blank slug of casing material are used respectively to identify hard metallic material having low tensile strength, great hardness, high melting point and low coefficient of thermal expansion, such as a cemented hard metal carbide: and a block or substantially solid piece of metallic casing material which is deformable and has high tensile strength and a higher coefficient of thermal expansion than the nib material so that it will have high shrinkage characteristics and which has not been provided preliminarily with a substantial recess or cavity for reception of a nib.

It will thus be seen that the objects set forth above are attained by the present invention in an efficient manner. Since certain changes may be made in carrying out the above method without departing from the scope of the invention, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

Having described our invention, what we claim as new and desire to secure by Letters Patent, is:

1. The method of making a drawing die, comprising heating a blank slug of casing material to a forging temperature, forcing a hard metallic nib into said slug by compressive force to displace casing material while limiting lateral expansion thereof causing casing material to project above the upper end of said nib, and hot-forging the projecting portion of the casing material pansion thereof'causing casing material to project above the upper end of` said nib, hotforglng the projecting portion of the casing material over the upper end of said nib, and heat treating the resulting assembly to cause the casing material to place said nib under high compression.

3. The method of making a drawing die, comprising heating a blank slug of casing material to a forging temperature, placing the hot slug in a forging die for limiting lateral expansion of said slug during forging, centering a hard metallic nib upon said hot slug, forcing said nib completely into said slug by compressive force to thereby displace casing materialuntil it extends above said nib and forms a casing around said nib while preventing axial downward movement .of said casing material and thereafter ejecting the encased nib from said forging die.

4. The method of making a drawing die, comprising heating a blank slug of casing material to a forging temperature, placing the hot slug in a forging die for limiting lateral expansion of said slug, centering a hard metallic nib upon said hot slug, forcing said nib into said slug by compressive force to displace casing material causit to project above the upper end of said nib, and hot-forging the, projecting portion of the casing `material over the upper end of said. nib.

5. The method of making a drawing die, comprising heating a blank slug of casing material to a forging temperature, placing the hot slug in a f forging die for limitinglateral expansion of said slug, centering a hard metallic nib upon said hot slug, forcing said nib into said slug by compressive force to displace casingmaterial causing it to project above the ,upper end of said nib, hot-forging the projecting portion of the casing material over the upper end of said nib, and heat treating the resulting assembly to cause the casing material to place said nib under high compression.

6.' The method of making a drawing die, comprising heating a blank slug of casing material to a forging temperature, placing the hot slug in a forging die for limiting lateral expansion of said slug, centering a hard metallic nib upon said hot slug, said nib having a lower coefficient of expansion than said slug, forcing said nib completely into said slug by compressive force to displace casing material so that the entire sides' of said nib are surrounded by said casing material, guiding said nib during the said forcing operation, preventing axial downward movement of said casing material and thereafter ejecting the encased nib from said forging die.

7. The method of making a drawing die, comprising heating a blank slug of casing material to a forging temperature, placing the hot slug in a forging die for limiting lateral expansion of said slug, positioning above said slug a nib-centering member having a guideway, placing a hard metallic nib in the guideway, forcing said nib into said slug by compressive force to displace casing material causing it to project above the upper end of said nib, and hot-forging the projecting portion of the casing material over the upper end of said nib.

8. 'I'he method of making a drawing die, comprising heating a cylindrical blank slug of casing material to a forging temperature, placing the hot slug in a circular socket of a forging die adapted to limit lateral expansion of said slug, positioning a nib-centering guide ring of substantial thickness in the forging die socket above said slug,

placing a nib of hard metallic material in said ring, forcing said nib into said slug by compressive force to displace casing material causing it to project above the upper end of said nib, and hot-forging the projecting portion of the casing material over the upper end of said nib.

9, The method of making a drawing die, comprising heating a cylindrical blank slug of casing material to a forging temperature, placing the hot slug in a circular socket of a forging die adapted to limit lateral expansion of said slug, positioning a nib-centering guide ring of substantial thickness in the forging die socket above said it to project above the upper end of said nib, and utilizing said ring in cooperation with means for forcing said nib into said slug whereby the bottom face of said ring causes casing material to iiow over the upper end of said nib.

10. The method of making a drawing die, comprising heating a cylindrical blank slug of casing material to a forging temperature, placing the hot slug in a circular socket of a forging die adapted to limit lateral expansion of said slug, positioning a nib-centering guide ring of substantial thickness in the forging die socket above said slug, placing a nib of hard metallic material in said ring, forcing said nib into said slug by compressive force to displace casing material causing it to project above the upper end of said nib, and restraining the upward movement of said ring to cause the casing material to ow over the upper end of said nib.

ll. The method of making a drawing die, comprising heating a blank slug of steel casing material to a temperature between about l850 F. and 2000 F.; forcing a cemented hard metal carbide nib into said casing blank by compressive force to displace casing steel while limiting lateral expansion thereof so that the sides of said nib are surrounded by casing material, and cooling the steel to and maintaining it at about 800 F. until it shrinks to place said nib under high compression.

l2. The method of making a drawing die, cpmprising heating a blank slug of steel casing material of high compressive strength to a tempera-l ture between about 1850o F. and 2000 F., placing the hot slug in a forging die for limiting lateral expansion of said slug during forging, centering a cemented hard metal carbide nib upon said hot slug, hot-forging said nib into said slug by compressive force to displace casing steel causing it to project above the upper end of said nib, hotforging the projecting portion of the casing steel over the upper end of said nib, heat treating the resultant steel casing at about 800 F. to place said nib under high compression, and tempering the resultant die at a temperature between about 900 F. and 1250 F. i

13. The method of making a drawing die, comprising heating a blank slug of casing material to a forging temperature, placing the hot slug in a forging die for limiting lateral expansion of said slug, holding a hard, metallic nib substantially centered upon said slug by means permitting longitudinal movement of said nib while forcing said nib into said slug, forcing said nib completely into said slug by compressive force to thereby displace said casing material until it extends well above said nib while preventing axial downward movement of said casing material and thereafter ejecting the encased nib from said forging die.

EDGAR W. ENGLE. HERSHEL BRYAN DUNCAN. 

